Cyclopentadienyl transition metal compounds are of particular interest in the polyolefin industry today for their use as polymerization catalysts. For example both biscyclopentadienyl and monocyclopentadienyl transition metal compounds (particularly of groups 4, 5 and 6) are known to polymerize olefins when used in combination with an activator such as an alumoxane or a non-coordinating anion. As interest in this area of chemistry has grown, so has the interest in substituting the cyclopentadienyl rings to tailor the catalysts to obtain different and hopefully unique products. Thus there is a need in the art for methods to quickly, easily and cleanly (i.e. get very high conversion without a significant number of side reactions or isomers) produce substituted cyclopentadienyl groups that can be used as ligands for catalyst production.
A common method to obtain substituted cyclopentadienyl compounds is to convert a substituted pentafulvene to a cyclopentadienyl group. Pentafulvenes are known to react with nucleophiles to produce substituted cyclopentadienides. (The Chemistry of Double-bonded Functional Groups, edited by S. Patai, 1989, John Wiley and Sons, pg 1133.) The difficult thing however, is to obtain pure cyclopentadiene structures that do not have to be "cleaned up" or otherwise treated. One way to accomplish this is by using pure pentafulvenes. Known pentafulvene syntheses, however, have generally suffered the drawbacks of producing side reactions, isomers and low yields.
Thus new means to obtain pentafulvenes in high yield and purity, quickly, easily and cleanly is desired in the art.
The most widely used pentafulvene synthesis was developed by Theile in 1900 and consists of condensation of cyclopentadiene with aldehydes or ketones in the presence of NaOEt, NaOH, or KOH in alcohol. The Theile synthesis is described as giving good yields for aliphatic and alicyclic ketones, medium yields for diaryl ketones or alkyl aryl ketones but in most cases low yields for aliphatic aldehydes. (ibib, pg 1149.) Once the aldehydes are more sterically shielded then better results are obtained. For example a 70% yield of 6-substituted pentafulvene (R1 was 2,5,5-trimethylpentene-1 and R2 was H) was obtained by combining a sterically shielded pr electronically stabilized aldehyde with Li cyclopentadienide in THF. (ibid, page 1151, cf R. D. Little, et al J. Am Chem. Soc. 105, 928, (1981).) Further work suggests that high yields of pentafulvenes can be obtained if the reaction is performed in an excess of pyrrolidine (in methanol). (ibid, pg1152) and J. Org. Chem. Vol 49, No. 11 1984 pg 1849-1853. Pyrrolidine however is expensive.
Hill, Jensen and Yaritz synthesized fulvenes from indenes and flourenes combined with an aldehyde or a ketone using a phase transfer catalyst (tetrabutylammonium hydrogen sulfate) and solid sodium hydroxide without resorting to a Grignard or alkali metal derivative. J. of Chem. Ed. Pg 916, 1986.
This invention address the need for clean, quick high yield methods to produce pentafulvenes.